Known examples of the blow-molded foam include a climate control duct provided in an instrument panel of a vehicle. The climate control duct often employs a foamed duct formed by molding the foamed resin material. The foamed duct is light in weight. Such a foamed duct can be manufactured easily in a manner that, for example, the resin material such as polyolefin resin including a foaming agent is melted and kneaded and then a foamed parison extruded out of a die of an extruder is blow-molded.
The resin material used for the blow-molded foam is often polyolefin resin. In particular, polypropylene resin is generally used. In recent years, using polyethylene resin alternatively has been examined for the purpose of reducing the material cost (see Japanese Unexamined Patent Publication No. 2011-194700 A).
Patent Literature 1 has disclosed the duct for vehicles, which is obtained by adding a chemical foaming agent to a mixed resin obtained by mixing high-density polyethylene with a long-chain branched structure, a specific gravity of 0.95 to 0.96, a melt flow rate (MFR) of 3 to 7 g/10 minutes, and a melt tensile force of 100 to 250 mN and high-density polyethylene with a melt flow rate (MFR) of 0.3 to 1.0 g/10 minutes, and then blow-molding the resulting mixture.